On our previous boat, we had a B&G masthead unit that had ceased to function. It had it's microprocesor that had supposedly malfunctioned because of stactic discharge (like a micro lightning strike).

B&G replaced the masthead unit with a "new" one which was made with a carbon fiber frame. It is supposed to conduct such discharges to the mast and protect the little sensitive board in the masthead unit.

That may be your problem?